(a) Field of the Invention
The present invention relates to a continuous alcohol fermentation process using an immobilized yeast, in particular a continuous alcohol fermentation process which is so designed that a fixed amount of immobilized yeast is packed in a fermentor and a substrate solution is supplied to said fermentor so that it runs parallel with the immobilized yeast, thereby effecting a continuous alcohol fermentation.
(B) Description of the Prior Art
Alcohol (ethyl alcohol) is widely used for not only drinking but also various industrial purposes, and is manufactured by fermentation methods and synthesis methods. In the manufacture of alcohol on an industrial scale according to a fermentation method, where molasses is used as the starting material, part of said molasses is first diluted with hot water to such an extent as its total sugar content becomes about 15 wt./V%, a nutrient is added thereto, then the pH thereof is adjusted, and the same is sterilized. After completion of said sterilization, the same is cooled to about 30.degree. C., and then is inoculated with yeast fungus and cultured for about 2 days to prepare a seed culture (seed yeast). On the other hand, the remainder of said molasses is diluted with hot water to such an extent as its total sugar content becomes about 25 wt./V%, then the aforesaid seed yeast is added thereto, and thus fermentation is conducted at about 30.degree. C. The fermentation is completed in about 4 days and about 13 vol.% alcohol is prepared. Successively, the yeast is removed from the obtained alcohol broth and the latter is distilled to obtain alcohol (ethyl alcohol).
However, the fact is that the aforesaid manufacture of alcohol according to ferementation method is conducted in a batch culture, and that said batch culture includes drawbacks or disadvantages, for instance: (1) Since the yeast concentration is in a low range such as 3-4 g/l, a large fermentor capacity is needed in order to produce alcohol in a desired amount; (2) Since the reaction speed is slow, the fermentation time is prolonged and consequently the productivity is decreased, (3) Since the alcohol and the other by-products strongly retard the reaction speed, the concentration of product alcohol is naturally reduced from the viewpoint of manufacturing alcohol economically, and the like.
In order to solve these problems and profitably carry out the manufacture of alcohol according to a fermentation method, there have been proposed various methods, for instance, conducting the manufacture of alcohol continuously while dispersing yeast in a substrate solution, preparing an immobilized yeast by immobilizing a living yeast on a carrier and utilize this immobilized yeast in a living or growing state, and so forth.
The alcohol fermentation method using this immobilized yeast has been proposed very recently. A continuous alcohol manufacturing method is disclosed which comprises supplying a glucose-containing nutritional medium to an immobilized yeast obtained by immobilizing a concentrated yeast (Saccharomyces carbergensis) with carrageenan, or a concentrated yeast (Saccharomyces cerevisiae) with polyacrylamide (see "Kagaku Kozyo" (Chemical Factories) vol. 23, No. 3, pp. 26-30 published by Nikkan Kogyo Shinbun Sha).
The continuous culture to be practiced without immobilizing yeast as above mentioned, namely, while dispersing yeast in a substrate solution, and the continuous culture using immobilized yeast may be expected to be more profitable than the conventional batch culture in that alcohol can be manufactured in a relatively short time and consequently the fermentor can achieve a high volumetric efficiency (alcohol productivity of fermentor per unit volume and unit time). Among these continuous culture methods it is considered that the continuous culture using an immobilized yeast is more profitable.